In wireless communication systems, the network may choose to deploy New Radio (NR, often referred to as 5G) on adjacent or overlapping spectrum with LTE, i.e., NR waveforms and LTE waveforms are either transmitted on adjacent carriers/bands or on the same carrier/band. For the case where NR and LTE are deployed on adjacent carriers/bands, because of the way spectrum is allocated, a time division duplex (TDD) New Radio band is sometimes allocated next to a frequency division duplex (FDD) LTE band.
When this occurs, because of the possibility of out-of-band interference, there needs to be a guard band between the TDD New Radio band and the FDD LTE band, as otherwise the New Radio band cannot be used as a time division duplex (TDD) mode band. What results is a New Radio FDD downlink or TDD supplementary downlink (SDL) band that can be referred to as a “standalone” or “orphaned” band in that it has no corresponding uplink frequency. However, for a band to be of practical use for communications with user equipment, both downlink and uplink communications are needed.